Many on-line services require a user identification and authentication when the latter whishes to access a private part of such service, for instance to access its Facebook™ space or to be able to read its messages. In order to do this, the user is required by the server of said service to give an identifier and a password.
These data are verified with those of reference stored by the server, on the one hand for checking that the identifier is well indexed in the server and on the other that the password corresponds to that of reference. Once these verifications had been done, the server authorizes the access to the service to said user.